allow trema-switch to start without any ports option
remove ports default option value
fix crash when invalid group id accessing group stats
return error on invalid port no in port stats
rework statistics to comply with specification
Raise if the argument of Hellow.new() is not a Number.
::Hello -> Trema::Hello
add a default value for version in hello message
Merge branch 'master' of https://github.com/trema/trema-edge